In the aircraft industry, in ship construction and in the building field, increasing quantities of metal plates and especially large-area metal plates of sizes of 2 m.times.6 m and thicknesses of 3 mm to 15 mm are used. In the past, such metal plates could be formed in part by a hot rolling and, following the cooling steps in the hot rolling process, tended to have natural stresses. These could be largely eliminated by a heat treatment. After this heat treatment, tempering and cooling, the metal plates were generally no longer planar.
Because of the strict requirements for planarity for such plates, the metal plates were generally subjected to leveling in stationary roll-levelers and tension-levelers in a discontinuous manner. During mechanical handling and especially during machining operations resulting in material removal, the metal plates tended to develop faults and bulges which resulted in a loss of planarity and which could not satisfactorily be eliminated by local leveling operations.
By and large the tension-leveling of the individual plates was effected above the yield point to achieve a sufficient degree of freedom from internal stresses.
During the heat treatment and during the tension-leveling, the metal plate must be clamped under tension and the same applies in the cutting of the metal plates into smaller pieces or desired shapes. Where the metal plate was clamped, frequently along an entire edge of the metal plate, e.g. the length or width, the clamped portion was cut off to eliminate any defects resulting from the clamping engagement with the plate. The same applies for the transition regions between the clamping zones and the remainder of the plate so that throughout a constant cross section of the plate can be assured.
This gives rise to substantial losses of the steel or other metal of the plate. For all of these additional steps, corresponding transport and storage of the metal plates is required, thereby increasing the production cost and making the prior method of producing such plates relatively uneconomical.